Flow sensors may be used for measuring flows of any fluid such as liquids or gases. Such flow sensors may not be arranged directly in a main channel which main channel conveys the bulk of the fluid. Instead, the flow sensor may be arranged in a bypass bypassing the main channel into which bypass a portion of the fluid is diverted from the main channel. As a result, the flow sensor measures the flow of such portion of fluid in the bypass. The flow in the bypass in turn is a measure of the flow in the main channel which flow in the main channel can be derived by suitable conversion factors from the flow in the bypass. The arrangement of the flow sensor in the bypass may be owed to a better accessibility, e.g. for taking readings from the flow sensor, or for repair and/or exchange purposes, or to a better resolution in the measurement.
For the reason that the bypass is designed to only accept a small portion of the overall fluid conveyed in the main channel, the bypass dimensions are small compared to the dimensions of the main channel. Hence, the bypass generally is more susceptible to contamination. Such contamination may include particles contained in the fluid as conveyed in the main channel which may enter the bypass. Such particles may either become stuck in the bypass and, therefore, increase the flow resistance in the bypass or adversely impact the flow sensor itself. Both alternatives lead to incorrect measurement results which do not represent the real flow in the bypass and the main channel respectively.